The present invention concerns a system or device for two-sided coating of a paper web.
Devices of this type are described, for example, in the following papers:
(1) DE Pat. No. 29 15 300 PA0 (2) FI Patent Application No. 83 0674 PA0 (3) FI Patent Application No. 83 3306 PA0 (4) Sivert Westerg.ang.rd: "Twostream Coater--Versatile New Tools for Coating in Spotlight", Paper Age, May 1984.
A problem in the prior-art devices has been the inability to produce a faultless coating also on the face of the web facing the roll. The present invention can be fitted to a coating device of the type described in cited papers (1) to (4).
In the so-called Billblade-type coating device of the cited paper No. (1), attempts have been made to solve this problem so that the web is detached from the roll immediately after the coating blade. This solution has, however, caused the problem that the coating device becomes highly sensitive to variations in the tractive load on the web after the coating blade. An excessively high tractive load causes tearing, an excessively low tractive load again makes the web follow along with the counter roll, in which case the coating facing the roll becomes damaged. Moreover, on the roll-side face of the web, at high speeds (.gtoreq.600 m/min) "mist" is formed, which likewise damages the roll-side coating.